The present invention relates to a friction component such as a brake lining or a clutch facing, and in particular, to an apparatus and method for manufacturing a friction component in which that portion of a friction material which is attached to a back plate has a multilayer structure.
Many friction components such as brake linings and clutch facings constitute the products by attaching to a friction material a metal plate called a back plate, as in brake shoe assemblies, clutch disc assemblies, or disc pads; however, some products, such as brake linings, are made of friction materials alone.
In addition, the friction material is formed by mixing together a fibrous material, a filler, and a binder. A powdery material comprising a mixture of these materials is placed in a molding box and pressurized and heated by a press machine to form a friction component. Two methods are used for molding: one uses a press machine to mold a temporary molding from a powdery friction material, uses another press machine to place the temporary molding on the back plate, and then pressurizes and heats the molding for adhesive molding, and the other directly attaches a powdery friction material to a back plate using a press machine.
The term xe2x80x9cfriction component,xe2x80x9d used herein, refers not only to a friction component with or without a back plate but also to a temporary molding unless otherwise specified.
Methods for adhering the friction material and the back plate together include the provision of an adhesive layer or the use of a binder contained in the friction material. If an adhesive layer is formed, a two-layer structure is used.
A conventional molding of a two-layer structure is obtained by measuring the weights of a friction material and an adhesive-layer material, both powdery, spreading the adhesive-layer material throughout a mold in such a way that the material has uniform thickness, placing the frictional material on the adhesive-layer material, and using a press machine to pressurize the materials in order to form a temporary molding. If no temporary molding is used, the adhesive-layer material and the friction material are placed next to another, a back plate is placed into direct contact with the adhesive-layer materials, and a press machine is used to pressurize and heat the materials for molding.
The conventional method, however, measures the weights of the powdery materials used to form the adhesive layer and manually or automatically levels predetermined amounts of the materials in such a way that they have a uniform thickness, so the thickness of the layer varies significantly. Normally, the thickness of the friction material is about 10 to 25 mm, whereas the adhesive layer is thin and has a thickness of 1 to 2 mm. If variations in thickness result in an excessively thin layer portion, the adhesive strength of this portion becomes insufficient. In addition, the conventional technique fails to provide a uniform thickness, so the adhesive layer is formed to be generally thick to prevent the declines in adhesive strength associated with thin layer portions.
Thick portions of the adhesive layer are also prone to problems. In such a portion, if the friction material becomes worn, the adhesive layer is exposed excessively early, thereby degrading elements of friction performance such as friction coefficient, wear, and fade resistance.
With respect to the friction material placed on the adhesive layer, the properties required for the surface side pressed against a disc are not the same as those required for the side closer to the back plate. For example, even in the same friction component, the surface side requires friction characteristics such as a stable friction coefficient and biased-wear resistance, while the side closer to the back plate requires strength-related characters such as toughness and cracking resistance. Thus, the friction materials are desirably structured to have multiple layers that meet the requirements for the respective portions. To achieve this, a plurality of types of powdery friction materials having different compositions are provided and placed on one another in a predetermined order to form a multilayer structure.
It is difficult, however, to provide each layer with the specified thickness when the above conventional method is used to provide a multilayer structure.
This invention is proposed to solve this problem, and its object is to provide a friction component manufacturing apparatus and method for providing a friction component for a multilayer structure having two or more layers wherein each layer can be formed so as to have a specified thickness. It is another object of this invention to provide a friction component suitable for use in this manufacturing apparatus and method.
To achieve these objects, this invention provides an apparatus for manufacturing a friction component having a multilayer structure by feeding sequentially two or more types of powdery materials into a molding box, executing either vertical pressurization or pressurization and heating between a fixed mold and a plunger that can elevate up and down into the molding box, so as to form a temporary molding or a molding, characterized in that a slide plate having a void of a predetermined shape formed therein is provided between the molding box and the fixed mold, in that a hopper for the powdery materials having an output port is provided on the slide plate, and in that the slide plate can be moved in the horizontal direction so that the output port is open over the void in the slide plate while being blocked at other positions.
In addition, the void may be a hole formed so as to penetrate the slide plate and a bottom plate that blocks the bottom of the hole may be provided so as to slide over the slide plate. The slide plate and/or said bottom plate may constitute a split mold. A back plate holding section in communication with the void may be formed in the lower part of the slide plate.
Alternatively, one or two or more slide plates may be placed on said slide plate so as to move independently in the horizontal direction. A hole constituting part of the void may be formed in each of the overlapping plates so as to penetrate them. A bottom plate blocking the bottom of each void may be slidably provided. A hopper for the powdery material having an output port may be provided in each slide plate. The output port may be open over the void in the slide plate while being blocked at the other positions.
The present method for manufacturing a friction component having a multilayer structure by executing either vertical pressurization or pressurization and heating between a fixed mold and a plunger that sequentially feeds a plurality of types of powdery materials into a molding box so as to form a laminate and that can elevate up and down into the molding box, is characterized in that the method comprises using any of the above friction component manufacturing apparatuses to move one, two or more slide plates in the horizontal direction in order to move each void beneath the output port in the corresponding hopper, thereby enabling the powdery materials in each hopper to be dropped into the void; moving the slide plates in the horizontal direction to allow the output port to be used as a leveling plate to sufficiently fill each void with the powdery material; moving all voids beneath the molding box in such a way that the voids overlap the molding box; feeding a predetermined amount of the final powdery material into the molding box; and executing either pressurization or pressurization and heating between the plunger and the fixed mold to temporarily or otherwise mold a friction component of a multilayer structure.
In this case, the bottom layer of the friction component may be an adhesive layer.
A friction component according to this invention is characterized in that a friction component of a multilayer structure has at least one layer containing 4% or less of fibrous components of 500 xcexcm or more fiber length. Alternatively, the layer containing 4% or less of fibrous components of 500 xcexcm or more fiber length may further contain 2 to 30% of adhesive organic filler. The layer containing 4% or less of fibrous components may be an adhesive layer, and 1.5 to 3.0% of the 4% of fibrous components may be metal fibers.